1. Field of the Invention
The present invention relates to a medical system.
2. Description of the Related Art
Recently, in ophthalmic sites, an apparatus called an optical coherence tomography (to be referred to as an OCT hereinafter) has been introduced. This apparatus can obtain a volume image constituted by a plurality of two-dimensional tomographic images of the retina.
In ophthalmic sites, users (technicians and doctors) interpret a layer structure from a volume image and observe the states and distribution of lesions and the three-dimensional running of fundus blood vessels. It is therefore necessary to display the distribution of lesions and blood vessels by using volume images so as to facilitate observation.
As a technique for implementing such a display, volume rendering is known, which assigns opacities to voxels in accordance with an opacity function, and performs translucent display of target volume data, thereby visualizing an internal structure. In general, the user generates an opacity function by manually setting the shape and the position of a peak, width, and the like of a function by using a user interface. Japanese Patent Laid-Open No. 2008-006274 discloses a technique of automatically generating such an opacity function. This technique fits a Gaussian function to a CT value histogram and can opaquely display the range of CT values calculated from the average value and standard deviation of the resultant data.
In this case, the following problems arise in the arrangement configured to automatically generate an opacity function to perform volume rendering for easy observation of tissues in a volume image of the retina.
Consider a case in which blood vessels are displayed. In this case, in a tomographic image obtained by OCT, the luminance value of a blood vessel region is high. Since a region near the lower end of the nerve fiber layer in which blood vessels run has a high luminance value, the contrast of the region in which blood vessels run is low. This makes it difficult to facilitate observation of blood vessels by volume rendering using an automatically generated opacity function.
Consider a large number of white spots distributed in a layer below the nerve fiber layer and a layer above the retinal pigment epithelium. The luminance values of white spots are high like those of these layers. For this reason, even if the luminance values are converted into opacities, the nerve fiber layer and the retinal pigment epithelium located outside the white spots are displayed, and the white spots located inside them are difficult to display.
When displaying tissues (blood vessels and white spots) of the retina based on a tomographic image captured by OCT in this manner, even if an opacity function is automatically generated, the tissues may not be effectively displayed to the user (technician or doctor).